British light-heavyweight Buatsi earned a win yet underwhelming start to his career under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic medal winner's work rate likely gained him a split decision in a competitive ten-round bout at the boxing arena.
But the challenger found success, delivering effective clean blows in a fight where the approaches failed to mesh, with excessive holding marring the contest.
The scoring judges had it 96-94 for to Buatsi, with the third a 95-95.
"It wasn't my greatest display but what defines champions? They prevail," Buatsi stated in the ringside as he was greeted with disapproval from the audience.
The British fighter returned to winning ways after his first professional defeat - an thrilling contest with Callum Smith in February - to claim a twentieth professional win.
Some ringside observers thought Parker, 31, merited the decision but the British boxer experienced the second setback of his 28-match professional journey.
The Champion Earns Triumph in Slow Encounter
The fighter's advancement has slowed in recent times through contract problems and considerable time of inactivity.
Previously predicted as the rising talent of UK boxing, he now stands trying to realize his potential - maybe in what seems like a last chance - under recent support.
He started carefully, with both competitors willing to be aggressive in a cagey early stages.
Parker, whose single earlier setback came at super-middleweight against John Ryder in two years ago after damaging his hand during the bout, was competing in only his second appearance at light-heavyweight.
By the middle rounds, Parker had stayed in contention, making life awkward for Buatsi, who utilized a tight guard to barely take the better rounds.
The spectators' acceptance diminished because of frequent holding, with the challenger going down several times during close exchanges.
Parker closed well, but several stanzas were hard to judge. Although, previous titleholder the boxing analyst - providing analysis for Dazn - had it strongly leaning for Parker, giving Buatsi just a single round.
The victor advances, but with the presence of power puncher Benavidez, and Eastern European fighter Bivol ruling the division, the road to world glory - judging by this showing - still looks steep.
Hatton Tribute Fuels All-Manchester Fight
In the co-main event, Arthur defeated Rea by divided decision in a excellent all-Manchester battle to win the European light-heavyweight title.
The arena fell silent for a deeply poignant tribute prior to the bout as ten bells tolled in honor of the city's native Hatton, who died 46 years old in last month.
It was the initial significant broadcast fight night in the urban center since Hatton's passing. As the concluding sound ended, the quiet became a shout of "there's just one Ricky Hatton".
The fighting during the bout equaled the feeling. Arthur was knocked down by a significant blow squarely on the face in the second round, rising shakily to his footing on the count of eight.
But the Manchester United-red shorts of Arthur soon advanced again. On the opposite side, the opponent - in opposing blue - was marked up quickly, noticeable damage forming under his eye as the duo exchanged hard punches.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, fought fire with fire with powerful upward punches as the pace seldom decreased over twelve rounds.
Arthur barely secured the verdict with judges scorecards of draw, close margin and wider gap, but each competitor were relentless and brave, all the qualities their idol the legend represented.
